Dyeing of cellulose

ABSTRACT

Dyed cellulosic regenerated elongate members such as fibers are produced by dyeing the regenerated members with a cationic direct dye after formation but before first drying. A method of producing the dyed elongate members comprises forming a dope containing cellulose or a cellulose compound in solution in a solvent, extruding the dope through at least one orifice into a bath containing water to form an elongate extrudate from which solvent is dissolved and/or the cellulose compound is converted to cellulose so as to form the elongate member, dyeing the formed but never dried elongate member with a cationic direct dye and optionally also with an anionic direct dye and then drying for the first time the dyed elongate member.

TECHNICAL FIELD

This invention relates to dyeing and has particular reference to thedyeing of cellulosic elongate members, particularly cellulosic fibres.It has further particular reference to the dyeing of cellulosic fibresspun from a solution containing cellulose or a cellulose compound.

BACKGROUND ART

Cellulosic fibres formed by spinning a solution or dope are well known.Cellulosic fibres of the viscose type have been manufactured for manyyears by dissolving sodium cellulose xanthate in caustic soda to form asyrup-like spinning solution known as viscose and commonly referred toas a spinning dope. The spinning dope is spun by extruding it throughfine holes into a coagulating bath of sulphuric acid and salts whichneutralise the alkaline content of the viscose dope and regenerate theoriginal cellulose as continuous filaments. If the orifice through whichthe viscose dope is extruded is an elongate slit it is possible tomanufacture a thin sheet of cellulose. If the orifice is annular it ispossible to manufacture a tube of cellulose.

Such cellulosic regenerated elongate members are extremely well known.

In more recent years it has been proposed to manufacture cellulosicregenerated elongate material by forming a true solution of cellulose ina solvent such as a tertiary amine N-oxide. The tertiary amine N-oxidecellulose solution is then extruded into a water bath to dissolve outthe amine oxide and to re-form the cellulose in a continuous filament orstrip or tube depending on the shape of the orifice through which thematerial has been extruded.

DISCLOSURE OF THE INVENTION

It has now been discovered that such cellulosic regenerated material maybe dyed by a route which in its most preferred form involves very lowpollution levels, is very economic and is very quick.

The cellulose solution may be a solution of cellulose in an amine oxidesolvent. Examples of such amine oxides are tertiary amine N-oxides suchas N-methylmorpholine N-oxide, N,N-dimethylbenzylamine N-oxide,N,N-dimethylethanolamine N-oxide, N,N-dimethylcyclohexylamine N-oxideand the like. The use of amine oxides in processes for dissolvingcellulose is disclosed in U.S. Pat. Nos. 3,447,939, 3,508,941 and4,246,221, the contents of which are included herein by way ofreference.

By the present invention there is provided a method of dyeing acellulosic regenerated elongate member which includes the steps of:

(i) forming a dope containing a material selected from the groupconsisting of:

(a) cellulose in solution in a solvent, and

(b) a cellulose compound in solution in a solvent,

(ii) extruding the dope through at least one orifice into a bathcontaining water to form an elongate extrudate from which either:

(a) solvent is dissolved to form the cellulosic regenerated elongatemember, or

(b) the cellulose compound is converted to cellulose to regenerate thecellulosic material and thereby form the cellulosic regenerated elongatemember, and

(iii) drying the cellulosic regenerated elongate member, characterisedin that the cellulosic regenerated elongate member is dyed with at leastone cationic direct dye after formation but prior to first drying.

A cationic direct dye comprises a long planar molecule containingpositively charged groups. The long planar shape to the molecule enablesit to lie closely alongside the cellulose molecule and to bond to themolecule by means of van der Waal's forces and hydrogen bonding. Thepositively charged groups on the dye can bond with O⁻ ions on thecellulose molecule.

It appears that dyeing the cellulosic member, particularly fibre, afterit has been formed but before it has been first dried (herein"never-dried cellulosic material") produces unique and improvedproperties in the material compared to products which are dyed afterfirst drying. There is also considerable energy saving and saving inchemicals to be achieved, as well as enhanced uniformity of the dyedmaterial.

In addition to treatment of the never-dried cellulosic material with thecationic direct dye, a subsequent treatment with an anionic direct dyemay be used to produce further bleed-fastness characteristics byreaction between the anionic and cationic dye molecules.

The present invention also provides a cellulosic regenerated elongatemember which has been dyed with a cationic direct dye whilst still inthe never-dried condition.

The pH of the solution for the cationic direct dye may for example be pH3, pH 4, pH 4.5, pH 5, pH 6, pH 7, pH 8, pH 9, or pH 10. The dyestuffsmay be applied at ambient temperature or at an elevated temperature. Theelevated temperature may for example be 30°, 40°, 50°, 60° or 70° C.Alternatively, the elevated temperature may be closer to the boilingpoint.

The cationic direct dyes may be applied directly from water or from anyother suitable solvent. Preferably the solvent is an aqueous solvent.

The present invention further provides that the dyed cellulosic materialmay be dried as a continuous tow and cut to staple after drying or maybe cut wet to form staple and dried as staple.

Suitable cationic direct dyes for carrying out the invention are thosedyes available from Sandoz under the trade names "Cartasol Yellow K-GL","Cartasol Turquoise K-GL", "Cartasol Yellow K-3GL", "Cartasol OrangeK-3GL", "Cartasol Blue K-RL", "Cartasol Red K-2BN" and "CartasolBrilliant Scarlet K-2GL". Suitable dyes are also available from BASFunder the trade names "Fastusol Yellow 3GL" and "Fastusol C Blue 74L"."Cartasol" and "Fastusol" are believed to be Registered Trade Marks.

Other cationic direct dyes may be simply tested to see if they givesatisfactory levels of fastness for both light and wash tests.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example embodiments of the present invention will now bedescribed with reference to the accompanying drawings, of which:

FIG. 1 is a schematic view of a spinning, dyeing and drying system inaccordance with the present invention,

FIG. 2 is a typical cationic direct dye structure,

FIG. 3 is a schematic view of hydrogen bonding occurring with a fibrestructure and a cationic direct dye,

FIG. 4 is a typical basic dye structure, and

FIG. 5 shows hydrogen bonding of a basic dye to a schematic fibrestructure.

In all of the tests referred to below the fibres were dyed underlaboratory conditions. A predetermined percentage of dye was pipettedfrom a stock solution into a jar and a standard volume of water added.If the pH was required to be higher than 7 sodium carbonate was added toincrease the pH; if the pH was required to be lower than 7 acetic acidwas added to reduce the pH. The dye solutions were then heated to thepredetermined temperature. The tests were then carried out by puttinginto the jar the fibre which also had been heated to the sametemperature as the solution, sealing the jar and shaking until maximumexhaustion of the solution was achieved. Typically, dyeings took between20 seconds and 3 minutes to reach a maximum exhaustion. It should benoted that these laboratory scale dyeings take longer than real on-linedyeing because the concentration of the dyestuff in the dye bath is muchgreater in on-line dyeing. The time period of 20 seconds to 3 minutes ona laboratory scale corresponds to a satisfactory speed for on-linecontinuous dyeing of never-dried fibres.

It should be noted that no additions of salt (sodium chloride) were madeto the dyestuffs.

After dyeing, the fibres were rinsed under cold running water until nomore dyestuff was apparent in the water. For wash-fastness tests thesamples were heated to 60° C. in a mixture of soap and sodium carbonatein accordance with the ISO 3 standard wash-fastness tests. To determinelight-fastness the samples were rated against the British Society ofDyers and Colourists blue scale in which the higher the number the moreresistant is the material to light-fading. On a practical basis it isgenerally accepted that materials having a light-fastness of 4 areacceptable for apparel purposes. The light-fastness tests were carriedout to standard 5 only--suitable for apparel purposes.

Table I below shows the results of a series of 3 dyes carried out onnever-dried fibre under a series of alternative pH conditions.

                  TABLE I    ______________________________________                    Fastness on             Light  Fibre        Dyeing               Fastness         Wash   Conditions    Dye        on Paper Light   ISO 3  on Fibre    ______________________________________    Cartasol Blue               2-3      a) 3-4  a) Good                                       a) Room Temp.    K-RL (tietall       b) 3-4  b) Good                                       pH 4.5    complex Dye)                       b) Room Temp.                                       pH 8.0    Cartasol   2-3      4-5     Good   Room Temp.    Turquoise K-GL                     pH 4.5    (Phthalo-    cyanine Metal    Complex Dye)    Cartasol   3        a) 5    Not    a) Room Temp.    Yellow K-GL         b) 5    tested pH 4.5    (Cationic                          b) Room Temp.    Azo Dye)                           pH 5.5.    ______________________________________

By comparison, the light-fastness of the same dyes on paper is given andit can be seen that the dyes do not produce the same degree oflight-fastness on paper. Paper is a cellulosic material which may beregarded as pre-dried. It can be seen therefore that although thecationic direct dyes do not produce a particularly light-fast result onpaper they do produce light-fast results which are acceptable forapparel purposes on never-dried cellulosic materials.

It is not clear why the cationic direct dyes shown in Table I producebetter results on never-dried fibre compared to paper. Given that thedyes are believed to react with the fibre and to bond to the fibre byvan der Waal's forces it is not at all clear why this difference shouldappear. If the light-fastness of the dyes on paper were to be taken asindicative it would not be acceptable to use these dyes on fibres foruse in apparel. Fortunately, however, it has been discovered that thecationic direct dyes do produce a simple means of dyeing cellulosicmaterial on-line in the never-dried condition. Prior to the making ofthe present invention it had not proved to be a practical business todye cellulosic regenerated fibres on-line. Typically, cellulosic fibreshave been dyed after manufacture into fibre or as fabric or as yarn.

A further important factor in the use of a practical dyestuff is theability of the dye to resist backstaining when dyed fibre is washed withanother material. Thus, if dyed cellulosic material is washed with anylon material it is important that the dye does not transfer to thenylon and stain the nylon in the wash. The normal method of determiningthis backstaining is to wash a mixture of dyed fibres and fibres ofanother material in an ISO 3 wash test and determine the staining of theother material. In such a test values of 3-4 are acceptable for mostapparel uses and a value of 5 is normally considered suitable for allapparel uses.

Backstaining test results are given in Table II below. Also included inTable II are light-fastness tests. It can be seen that although BrownK-BL has good backstaining test results, better than Blue K-RL except onnylon, its light-fastness results are not quite as good. It will beappreciated that for a dye to be commercially acceptable a balance ofproperties is required and that, because of the complexity of dyestuffchemistry, occasionally one or more dyestuffs in a class will not havethe complete range of properties required even though the remainingdyestuffs in that class have an acceptable balance. Such oddities caneasily be determined by experiment and do not detract from the value ofthe invention as a whole.

                                      TABLE II    __________________________________________________________________________               Backstaining Wash Test (ISO 3)                                          Light Test    Cortasol dyes             pH               Acetate                    Cotton                        Nylon                            Polyester                                 Acrylic                                      Wool                                          (Fibre)                                              (Paper)    __________________________________________________________________________    Turquoise K-GL             5.5               4-5  4   4-5 4-5  4-5  4-5 4-5 2-3    (phthalocya-    nine metal    complex)    Red K-2BN             8.0               4-5  4   4   4-5  4-5  4-5 3-4 2    (azo)    Blue K-RL             8.0               4-5  3   4-5 4-5  4-5  4-5 3-4 2-3    (metal    complex)    Brown K-BL             8.0               4-5  4-5 3-4 4-5  4-5  4-5 1-2 2    (azo metal    complex)    __________________________________________________________________________

In Table II all dyestuffs were applied to the solvent-spun cellulosicfibre at 1% by weight of dry fibre. The dyestuffs were applied at roomtemperature and at the pH identified in the Table. In the case of thebackstain wash test, 1 g of dyed solvent-spun cellulosic fibre waswashed as a hank in a standard ISO 3 wash programme with an SDC (Societyof Dyers and Colourists) multifibre strip, 4 cm long, of undyed,nominally white, fibres of the materials specified. After washing, themultifibre strip was dried and examined for backstaining.

It is also possible to treat the never-dried fibre with cationic directdyes and subsequently to treat with anionic direct dyes such as Pergasoldyes. (Pergasol is believed to be a Registered Trade Mark.) The two dyesthen react to form effectively a pigment embedded firmly in the fibre.

Attempts were made to see whether dyes of other types than cationicdirect dyes could be used to dye on a continuous basis cellulosicnever-dried fibres. A range of basic dyes was applied to cellulosicnever-dried fibre at pH 5.5. The dyes were substantive to the fibre inthat they were attracted to the fibre. Unfortunately, however, they hadlittle or no affinity for the fibre as they rinsed out almost completelyunder cold running water. As the dyes rinsed out so completely no wash-or light-fastness tests were carried out. The following dyes were triedas typical basic dyes:

Astrazon Golden Yellow GLE--C.I. Basic Yellow 28

Yoracryl Red BGL--C.I. Basic Red 46

Astrazon Red GTLN--C.I. Basic Red 18

Maxilon Blue GRL--C.I. Basic Blue 41

(Astrazon, Yoracryl and Maxilon are believed to be Registered TradeMarks.) Attempts were also made to see whether anionic direct dyes woulddye never-dried cellulosic fibrous material in the absence of cationicdirect dyes. A range of Pergasol dyes available from Ciba-Geigy and aParamine dye available from Holliday were applied to never-driedcellulosic fibre. (Paramine is believed to be a Registered Trade Mark.)Tests at pH 5 carried out at room temperature indicated that only paledyeing of the cellulosic fibre was obtained. Increasing the pH to 8 gavebetter results but still not as good as cationic direct dyeing. Thefollowing anionic direct dyes were tested:

Pergasol Orange 5R--C.I. Direct Orange 29 (azo)

Pergasol Yellow GA--C.I. Direct Yellow 1373 (azo)

Pergasol Turquoise R--C.I. Direct Blue 199 (phthalocyanine)

Pergasol Red 2G--C.I. Direct Red 329 (azo)

Pergasol Red 2B--C.I. Direct Red 254 (disazo)

Paramine Yellow R

The present invention therefore permits continuous on-line dyeing ofnever-dried cellulosic material.

A preferred material for on-line dyeing is the solvent-spun cellulosicfibre. A process suitable for carrying out the invention is illustratedin FIG. 1 of the accompanying drawings.

A mixture of cellulose, solvent such as amine oxide and water isprepared. The mixture is prepared as a slurry and then is heated undervacuum to boil off the water. The result of this is that the cellulosegoes into solution in the amine oxide to form a dope. Such processes forthe manufacture of a solution of cellulose in a solvent are welldescribed in the literature. The solution, commonly referred to as adope, is then injected through a pipe 1 into a jet assembly 2 containingmany fine holes. The jet assembly 2 is positioned over a water bath 3containing warm water 4. On emerging from the jet 2 the solution ofcellulose in amine oxide forms a plurality of gel strands and, as theamine oxide dissolves in the water bath 4, the gel strands form aplurality of filaments 5 of cellulose. The cellulose then passes througha series of water baths 6, 7 to remove more of the amine oxide. Thefilament 5 passes into a bleach bath 8 and is then washed in a series ofbaths such as bath 9 before passing into a dye bath 10. The dye bath 10contains a solution of a suitable dye such as Cartasol Blue K-RL, theexact concentration depending on the depth of shade required. Afterdyeing the never-dried filament, it is passed through a soft-finish bath11 before being passed to a drying system.

Two drying systems are shown in FIG. 1. The first drying system involvesfilament 12 passing around a pulley 13 to descend vertically as at 14into a staple cutter head 15. The wet filament 14 is cut by the head 15to form staple fibre 16 which is passed onto a moving bed 17 and theninto a drying tunnel 18. The dried staple fibre falls off the end of thebed as at 19 and is passed to a suitable packing machine.

Alternatively, the dyed filament may be passed along route 20 aroundpulleys 21 and 22 and then be dried as a continuous tow in a drying oven23 on heated drums 24. It can then either be plaited into a suitablepacking container 25 as a dry continuous tow of filaments or cut to formstaple for subsequent processing as a staple fibre.

A particular advantage of the route in which the fibre is dried as towand then cut to staple, as opposed to cutting whilst wet and drying, isthat it is easier to change colours whilst minimising contamination offibre of one colour with fibre of another colour. If coloured fibre iscut wet and dried, it is a very difficult and slow process to clean outthe staple fibre dryers before a different colour is dried.Contamination of the new colour fibre with the old is highly likely evenif the dryer is manually vacuum-cleaned between colours.

Drying the fibre in tow form means that only the fibre cutter anddownstream of the cutter has to be cleaned--a very much simpleroperation and one which means that the time spent with the machinerystopped between colours is much lower on fibre dried as tow as comparedto fibre dried as staple.

A further advantage of the colouring process of the invention, comparedto pigmentation processes used heretofore to colour viscose rayoncellulosics, is that the colours can be changed more rapidly, becausethe pigmentation route requires the pigment to be incorporated in thedope prior to spinning. Only certain pigments are suitable forincorporation in the dope, and the range of colours of such viscoserayon fibres is limited. It has also been normal practice with viscosefibre staple products to dry the fibre in staple form. This results inthe contamination problem referred to above.

It will be appreciated that by means of the present invention thecolouring of the fibre may be accomplished at little expense beyond themere cost of the dye. The washing baths used may simply be incorporatedinto the wash line for the fibre, and cationic direct dyes dye thenever-dried cellulosic fibre to a high standard of light- andwash-fastness with little production of unwanted waste chemicalproducts.

By way of identification a typical cationic direct dye structure isshown in FIG. 2 of the drawings and it can be seen that the molecule isessentially a planar molecule having cationic dye sites at 26, 27whereby the dye may bond to the anionic sites on the fibre.Schematically the hydrogen or van der Waal's bonding of the cationicdirect dye is illustrated in FIG. 3. For comparison, a typical basic dyestructure is shown in FIG. 4 and it can be seen that the physicalstructure of the dye is such that it cannot easily bond to thecellulosic molecule. A schematic arrangement of the basic dye bonding tothe fibre is shown in FIG. 5. It is believed that it is the physicalfailure of the basic dye to form a plurality of hydrogen bonds with thecellulose which results in poor fastness of the dye to the cellulosemolecule.

I claim:
 1. A method of manufacturing a dyed cellulosic regeneratedelongate member which includes the steps of:(i) forming a dope selectedfrom the group consisting of:(a) cellulose in solution in a solvent, and(b) a cellulose compound in solution in a solvent; (ii) extruding saiddope through at least one orifice into a water-containing bath to forman elongate extrudate; (iii) producing said cellulosic regeneratedelongate member by respectively either:(a) dissolving said solvent outof said elongate extrudate into said bath, or (b) regenerating saidcellulose compound to form cellulose; (iv) dyeing said cellulosicregenerated elongate member with at least one planar molecular cationicdirect dye; and (v) drying said cellulosic regenerated elongate memberfor the first time, said dyed cellulosic regenerated elongate memberhaving a backstaining resistance of at least 4 measured by the ISO 3wash test.
 2. A method as claimed in claim 1 further including the stepof dyeing said cellulosic regenerated elongate member with an anionicdirect dye subsequent to said dyeing step (iv) and prior to said dryingstep (v).
 3. A method as claimed in claim 1 wherein said cellulosicregenerated elongate member is dyed with an aqueous solution of saidcationic direct dye, the pH of said aqueous solution being in the range3 to
 10. 4. A method as claimed in claim 1 wherein said cellulosicregenerated elongate member is dyed with an aqueous solution of saidcationic direct dye, the temperature of said aqueous solution being inthe range ambient temperature to 70° C.
 5. A method as claimed in claim1 wherein said cellulosic regenerated elongate member is dyed with anaqueous solution of said cationic direct dye, said aqueous solutionbeing essentially free of added sodium chloride.
 6. A method as claimedin claim 1 wherein said dope is a solution of cellulose in a solvent,said solvent comprising a tertiary amine N-oxide.
 7. A method as claimedin claim 6 wherein said tertiary amine N-oxide is selected from thegroup consisting of N-methylmorpholine N-oxide; N,N-dimethylbenzylamineN-oxide; N, N-dimethylethanolamine N-oxide andN,N-dimethylcyclohexylamide N-oxide.
 8. A method according to claim 1wherein said cellulosic regenerated elongate member consists of fibres.9. A method as claimed in claim 8 wherein said fibres have the form of acontinuous tow in said drying step (v).
 10. A method as claimed in claim9 wherein said continuous tow is cut to form staple fibres subsequent tosaid drying step (v).
 11. A dyed cellulosic regenerated elongate memberhaving a backstaining resistance of at least 4 measured by the ISO 3wash test and having been dyed in the never-dried condition with aplanar molecular cationic direct dye.
 12. A dyed cellulosic regeneratedelongate member as claimed in claim 11 having been further dyed with ananionic direct dye in said never-dried condition subsequent to saiddyeing with said cationic direct dye.
 13. A dyed cellulosic regeneratedelongate member as claimed in claim 11 which consists of staple fibres.14. A dyed cellulosic regenerated elongate member as claimed in claim 11which has been prepared from a solution of cellulose in a solvent.
 15. Adyed cellulosic regenerated elongate member as claimed in claim 14wherein said solvent is a tertiary amine N-oxide.
 16. A dyed cellulosicregenerated elongate member as claimed in claim 15 wherein said tertiaryamine N-oxide is selected from the group consisting ofN-methylmorpholine N-oxide; N, N-dimethylbenzylamine N-oxide;N,N-dimethylethanolamine N-oxide and N, N-dimethylcyclohexylamineN-oxide.
 17. A dyed cellulosic regenerated elongate member as claimed inclaim 11 which consists of continuous filaments.
 18. A dyed cellulosicregenerated elongate member as claimed in claim 11 which consists of athin sheet or tube.